Spring autowired…pass source class to autowired class

Question

Caught up in a weird requirement. I need to attach unique error id to log4j message and return that message id back to interface.So, I though lets create a spring service, l

Answer 1

Why dont you use Spring AOP. AOP provides you much accessibility and features, and you can exploit its interesting features later also, when your application becomes heavy. Spring AOP

Answer 2

I used this mechanism to inject a logger.

Create this annotation..

/**
* Indicates InjectLogger of appropriate type to
* be supplied at runtime to the annotated field.
*
* The injected logger is an appropriate implementation
* of org.slf4j.Logger.
*/
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

@Retention(RUNTIME)
@Target(FIELD)
@Documented
public @interface InjectLogger {
}

Now lets define a class that actually does the job of injecting the logger implementation.

/**
 * Auto injects the underlying implementation of logger into the bean with field
 * having annotation <code>InjectLogger</code>.
 * 
 */
import java.lang.reflect.Field;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.util.ReflectionUtils;

import static org.springframework.util.ReflectionUtils.FieldCallback;

public class LoggerInjector implements BeanPostProcessor {

 public Object postProcessAfterInitialization(Object bean, String beanName)
   throws BeansException {
  return bean;
 }

 public Object postProcessBeforeInitialization(final Object bean,
   String beanName) throws BeansException {
  ReflectionUtils.doWithFields(bean.getClass(), new FieldCallback() {
   public void doWith(Field field) throws IllegalArgumentException,
     IllegalAccessException {
    // make the field accessible if defined private
    ReflectionUtils.makeAccessible(field);
    if (field.getAnnotation(InjectLogger.class) != null) {
     Logger log = LoggerFactory.getLogger(bean.getClass());
     field.set(bean, log);
    }
   }
  });
  return bean;
 }
}

Using it is even simpler. Just add the Logger annotation created above to the Log field in the required class.

import org.slf4j.Logger;

public class Demo {

 @InjectLogger
 private Logger log;

 public void doSomething() {
  log.info("message");
  log.error("Lets see how the error message looks...");
 }
}